Environmental Studies Lecture Notes #3 January 2023 Revision PDF

UNIVERSITY OF TECHNOLOGY FACULTY OF SCIENCE AND SPORT Module: Environmental Studies Lecture #3 BIOGEOCHEMICAL CYCLES Matter (the material of which organisms are composed) moves in numerous cycles from one part of...

UNIVERSITY OF TECHNOLOGY FACULTY OF SCIENCE AND SPORT Module: Environmental Studies Lecture #3 BIOGEOCHEMICAL CYCLES Matter (the material of which organisms are composed) moves in numerous cycles from one part of the ecosystem to another i.e. from one organism to another and from living organisms to the abiotic environment and back again (National Climate Assessment, 2014). These cycles are called biogeochemical cycles (bio – life, geo – earth, literal translation is life earth chemical cycles) or nutrient cycles. A nutrient is a substance an organism needs to live, grow or reproduce. There are two types of nutrients, macronutrients and micronutrients. Macronutrients refer to the nutrients needed in large quantities such as carbohydrates, protein, and fat. These nutrients provide your body with energy or calories. Micronutrients refer to the nutrients needed in smaller amounts. These are usually referred to as vitamins such as vitamins C and K and minerals such as iron and zinc (Ohio State University, 2024). Four of the major biogeochemical cycles of matter are the carbon cycle, nitrogen cycle, phosphorus cycle and the water cycle. Carbon Cycle Carbon is the basic building block for carbohydrates, fats, proteins and nucleic acids such as DNA. The main carbon source for living organisms is carbon dioxide present in the atmosphere or dissolved in surface waters. The major carbon reservoir is found in the earth’s rocks, followed by fossil fuels and ocean beds. The major processes occurring in the carbon cycle are: Photosynthesis. Plants use the process of photosynthesis to manufacture plant carbohydrates using carbon dioxide as a raw material. As such, photosynthesis is the only natural process that removes carbon dioxide from the environment- an excess of which, as you will learn later in the module, has been implicated as a factor causing global warming. This carbon is in turn passed on to animals when they eat plants during consumption. Respiration and decomposition. These processes return carbon to the atmosphere. Combustion. This also returns carbon to the atmosphere by the burning of coal, oil, natural gas and wood. Diffusion. This process moves carbon between the atmosphere and oceans. Burial and Compaction. Carbon may be deposited in the ocean or on land. Carbon that is deposited in shallow coastal waters in the form of shells and coral forms limestone (calcium carbonate). Plant material on land may be buried by soil depositing on them. The weight of the soil is what helps to compact this material and add pressure to it. Over millions of years under these conditions the plant materials are converted to coal. Animal materials in the ocean that are buried and compacted in the same manner turn into oil. Humans affect the carbon cycle by various activities which include deforestation, the clearing of grasslands and green areas and the burning of fossil fuels and wood sources. These activities serve to add excess carbon to the atmosphere, in the form of carbon dioxide, which contributes to global warming. Solutions to these activities include replanting trees to increase the absorption of atmospheric carbon during the process of photosynthesis. Using more renewable energy sources such as solar, wind and hydropower will also reduce the amount of carbon dioxide added to the atmosphere from the use of fossil fuels (National Geographic Education, 2024). https://byjus.com/biology/carbon-cycle/ Nitrogen Cycle Nitrogen is crucial for all organisms because it is an essential part of biological molecules such as proteins and nucleic acids. Although the atmosphere is composed of 78% nitrogen gas (N2), a two atom molecule, this N2 is so stable that it does not readily combine with other elements to form compounds. There are five major steps in the cycle:  Nitrogen fixation – This is the conversion of gaseous nitrogen (N2), to ammonia (NH3). Some of the ammonia may be converted to ammonium (NH4). In this process nitrogen gas is fixed into a form that organisms can use. Although N2 can be fixed by combustion, volcanic action and lightning, most nitrogen fixation is thought to be biological. Biological nitrogen fixation is carried out by nitrogen fixing bacteria in soil and aquatic environments. Nitrification – Ammonia not assimilated (absorbed) by the plant undergoes nitrification: this is the conversion of ammonium (NH4) and ammonia (NH3) to nitrate (NO3). This process is accomplished by bacteria in the soil. Nitrate is easily absorbed by the roots of the plants. Assimilation – This is where plant roots absorb either nitrate or ammonia that was formed by nitrogen fixation and nitrification and incorporates the nitrogen into proteins and nucleic acids. Ammonification – Plants and animals return the nitrogen compounds to the environment as waste when they die and are decomposed, or eaten, by detritus feeders. T he conversion of biological nitrogen compounds into ammonia is known as ammonification. This begins from waste products and the decomposition of organisms. The bacteria that perform these processes are called ammonifying bacteria. * Please note that after step 4 – Ammonification, the ammonia formed can be reintroduced into the cycle at step 2. Denitrification – This is the reduction of ammonia/ ammonium into nitrate and then nitrite to gaseous nitrogen. Denitrifying bacteria reverse the action of nitrogen fixing and nitrifying bacteria by returning nitrogen gas to the atmosphere (Science Learning Hub, 2024). https://pmgbiology.com/2014/04/12/bacteria-of-the-nitrogen-cycle-a-understanding-for-gcse-biology/ Humans affect the nitrogen cycle by using excessive amounts of nitrogen based fertilizer and adding nitrogenous gases to the atmosphere by burning fossil fuels. Excessive amounts of nitrogen and phosphorus can cause eutrophication in water bodies. Eutrophication is the over-nourishment of aquatic ecosystems with plant nutrients (mostly nitrates and phosphates) resulting from human activities such as agriculture, urbanization and discharges from industrial plants and sewage treatment plants. (Miller & Spoolman, 2010). Farmers can use more organic fertilisers (animal manure, green manure or compost) to reduce the potential for eutrophication. Organic fertilisers take a longer time to release nutrients into the soil because they have to be decomposed before the nutrients are available to plants. This reduces the potential of rain washing out all the nutrients into aquatic ecosystems. The solution to the production of nitrogen oxide caused by the burning fossil fuels would be to use more renewable energy sources such as solar, wind and hydropower since this will decrease the amount of nitrogen oxides released into the atmosphere. Phosphorus Cycle Phosphorus is an essential plant and animal nutrient, particularly for growth. It is used in the formation of bones, teeth, and animal and plant membranes. Phosphorus is a non-renewable resource and as such needs efficient use of the quantities available. The phosphorus cycle has no biologically important gaseous compounds. The processes involved in the cycle are:  Weathering: Rocks containing inorganic phosphates break into fragments through weathering. Erosion: Movement of the fragments or particles by ice, water, wind or animals. Runoff: Runoff is the movement of water along the land surface into surface bodies of water. As the water runs off the land, soil and dissolved phosphorus particles will enter the surface bodies of water e.g. oceans, rivers, lakes and streams Absorption: These inorganic phosphates are absorbed or ingested by an organism. Assimilation: Incorporation of the phosphorus into the cellular components of the organism. Consumption: Phosphorus enters other organisms through the food web. Decomposition: When the organism dies, phosphorus is released back into the environment as inorganic phosphate by decomposers. Leaching: Leaching is the removal of a solute by the action of a liquid (usually water) passing through the soil. Humans disrupt the phosphorus cycle by removing phosphorus from an area through the excessive mining of phosphate rocks to produce fertilizers and detergents and through the shipping of food from farms to cities where it is lost as effluent (sewage discharge). The use of excessive amounts of inorganic fertiliser that contain phosphorus results in eutrophication. Similar to the nitrogen cycle, farmers could use more organic fertilisers to reduce the potential for eutrophication. To combat the loss of phosphates from mining, composting (allowing vegetable matter to decay for use as nutrient rich soil) and the consumption of more locally produced foods is more likely to keep phosphates in the area from which it originates. By exporting food crops, the phosphates are lost from the areas from which they were taken, to the areas where the foods are sent. Replenishing the lost phosphates through importing fertilisers would be the only way of regaining the nutrients lost in that area (Science Learning Hub,2024). https://quizlet.com/gb/473042271/the-phosphorous-cycle-diagram/ Hydrological (Water) Cycle Only about 0.024% of Earth’s water supply is available and accessible as liquid freshwater. The rest is too salty for use, stored as ice (glaciers, icebergs), or is too deep underground to extract at affordable prices (Miller & Spoolman, 2010). Water continuously circulates from the ocean to the atmosphere to the land and back to the ocean, providing us with a renewable supply of purified water on land. Water moves from the atmosphere to the land and ocean in the form of precipitation (rain, snow, sleet, hail). Water evaporates from the ocean, from soil, stream, rivers and lakes to form clouds in the atmosphere. Transpiration from plants also contributes to cloud formation. This is loss of water from the stomata (pores) of plants. Evapo-transpiration refers to the sum of evaporation and transpiration. Condensation refers to the process of water vapour changing to water. The movement of water into the soil is known as infiltration. Water also percolates or seeps downward through the soil and rock to become ground water and aquifers. Water that does not evaporate or infiltrate the earth’s surface may flow along the land into rivers and streams in the process known as run-off. The area of land being drained by run-off is called a watershed. Sublimation is the term used when water moves from solid phase to gaseous phase without going through the liquid phase. Humans affect the hydrologic cycle by withdrawing large quantities of freshwater faster than it can be replaced, and by clearing vegetation. This can affect the cycling of water where some aspects of the cycle can be slowed or even stopped. Creating concrete barriers, buildings and pavements hinder infiltration and keeps more water above ground. This can lead to the reduced recharge of ground water, flooding, and soil erosion (Miller & Spoolman, 2010). Conservation efforts, recycling and reusing water will help reduce the need to withdraw large volumes of water. Using more porous concrete and asphalt, along with planned green spaces, will allow for more infiltration. This will reduce the potential for flooding and help replenish groundwater stores (Center for Science Education, 2024). Water/Hydrological Cycle https://expeditieaarde.blogspot.com/2011/11/water-cycle.html TUTORIAL QUESTIONS 1. What are biogeochemical cycles? Explain their importance to living things. 2. What is the main source of carbon for living things? 3. Identify the processes that extract carbon and return carbon to the atmosphere in the carbon cycle. 4. What are the three largest reservoirs of carbon? 5. Developed countries are largely responsible for environmental problems associated with disturbance of the carbon cycle and should therefore be made to solve the problems they have created. Discuss this statement giving examples to support your answer. 6. Explain the following processes of the nitrogen cycle naming the type of bacteria that may be involved in each process: Nitrogen fixation Nitrification Ammonification Assimilation Denitrification 7. a) What are the major steps in the phosphorus cycle? b) Discuss ways in which humans are affecting the phosphorus cycle. c) Explain why the phosphorus cycle may often be considered as coming to a dead end. 8. a) What are the major steps in the hydrological cycle? b) Discuss the importance of trees in named processes of the hydrological cycle. c) Suggest ways in which human overpopulation may affect the water cycle. d) Suggest ways to avert people’s negative effects on the hydrological cycle. 9. What is precipitation? List four forms of precipitation. 10. Explain the processes that purify water in the hydrological cycle. References National Climate Assessment (2014). Biogeochemical Cycles. Accessed May 26, 2024 from https://nca2014.globalchange.gov/report/sectors/biogeochemical-cycles Ohio State University (2024). Micronutrients vs. Macronutrients and where to find them. Access May 26, 2024 from https://health.osu.edu/wellness/exercise-and-nutrition/micronutrients-vs- macronutrients. National Geographic Education (2024). The Carbon Cycle. Accessed May 26, 2024 from https://education.nationalgeographic.org/resource/carbon-cycle/ Science Learning Hub (2024). The Nitrogen Cycle. Accessed May 26, 2024 from https://www.sciencelearn.org.nz/resources/960-the-nitrogen-cycle Science Learning Hub (2024). The Phosphorus Cycle. Accessed May 26, 2024 from https://www.sciencelearn.org.nz/resources/961-the-phosphorus-cycle Center for Science Education (2024). The Water Cycle. Accessed May 26, 2024 from https://scied.ucar.edu/learning-zone/how-weather-works/water-cycle Originally Compiled By: Raymond Martin First Revision Done By: Nikki Bramwell, Raymond Martin and Damian Nesbeth Updated By: Damian Nesbeth, August 2021